The invention relates generally to valves which control fluid flow through an orifice and are responsive to pressure conditions. More particularly, the invention relates to such valves which are fluidly connected to reservoirs or conduits of fluid which are to be maintained at a steady state pressure, whereby the operating mechanism of the valve is directly connected to the fluid reservoir and acts in response to pressure changes in the fluid reservoir. Even more particularly, the invention relates to such valves which are operated by hydraulic fluid acting on a piston, the piston and hydraulic oil connection being sealed by O-rings to allow for extended travel and the piston casing containing a conduit for high pressure air to be applied to the opposing side of the piston to move the piston against the pressure of the hydraulic fluid. Valves of this general type are known as compensating valves, where the valve acts to reduce or increase flow of fluid into or out of the fluid reservoir or conduit through an opening in response to changes in the pressure of the fluid in the fluid reservoir or conduit.
A compensating valve of a type similar to the present invention is disclosed in my U.S. Pat. No. 4,493,558, issued Jan. 15, 1985, wherein a compensating valve system which controls an adjustable homogenization orifice is shown. A homogenization orifice acts to homogenize two insoluble liquids through shear layer and cavitation effects such that they will remain mixed for a suitable period before separation. Shearing effects are the result of fluid flow past a solid object, which creates turbulence in the flow stream. Shear effects occur at low flow rate or pressure, and the degree of mixing of two liquids in the flow is limited. Cavitation is the formation of vapor or gas filled cavities in liquids by mechanical forces. More precisely, it is the formation of vapor filled cavities in the interior or on the solid boundaries of vaporizable liquids in motion when the pressure is reduced to a critical value without change in ambient temperature. In pipelines cavitation is a result of the combination of high flow rate and pressure drop from high to low. Cavitation also occurs in turbines, pumps and propellers. In many circumstances cavitation is to be avoided, as it lowers the efficiency of equipment, produces noise and vibration, and causes rapid erosion of boundary surfaces. On the other hand, cavitation can be very useful in producing homogeneous mixtures of insoluble liquids and solids in other liquids, as well as being a means to reduce particle size.
One application where shear effects and cavitation have been applied with positive effect is in the area of homogenization of fuel oil and water mixtures. It is known that effective intermixing of additional components such as fresh water into a fuel oil stream which is subsequently burned to operate a combustion system, such as a boiler or internal combustion engine, is advantageous with regard to reducing fuel consumption corrosion, particulate emissions and other pollutants, and soot build-up. As taught for example in U.S. Pat. No. 4,127,332, a stream of fuel oil is passed through a relatively small orifice at high velocity to create a cavitating free turbulent velocity shear layer, and water is added at the orifice exit, otherwise known as the base of cavitation, resulting in a homogenized mixture or colloidal suspension of the two components with long term stability and lack of separation. The cavitation creates a flow regime at the orifice exit where vapor bubbles form, expand, contract and violently collapse. The resulting high pressure shock waves produce excellent intermixing of the components.
The pressure differential between the pressure of the upstream fluid prior to passage through the cavitating orifice and pressure of the fluid downstream of the cavitating orifice is critical for optimum mixing. For a fuel oil/water mixture, a pressure differential of 10:1 is preferred. This means that, for example, fuel oil having a pressure of 300 psig on the inlet side of the cavitating orifice should be maintained at 30 psig on the outlet side of the orifice. However, changes in various factors such as volume, viscosity, upstream pressure, downstream pressure and fuel temperature will alter this pressure differential ratio in an active system. It is therefore necessary to monitor the active system and make adjustments to compensate for the changes to maintain the proper pressure differential, as preferred tolerances are in the plus or minus 2 psig range.
One known way to monitor and control an active flow system is through the use of a compensating valve, as shown for example in my U.S. Pat. No. 4,493,558, which is coupled with a pressure sensing means monitoring the low pressure side of the cavitating orifice. The compensating valve has a solid sliding barrier adjacent a fixed orifice, such that the barrier is moved responsive to changes in pressure in the downstream region to either increase the effective opening size by exposing more of the orifice, thereby increasing flow and raising pressure in the downstream region, or to decrease the effective opening size by blocking more of the orifice, thereby decreasing flow and decreasing the pressure in the downstream region. The pressure sensing means communicates directly with the compensating valve by hydraulic fluid, such that an increase in pressure in the downstream region forces hydraulic fluid against the reciprocating piston of the compensating valve, extending the sliding barrier relative to the fixed orifice to decrease the opening size. A decrease in downstream pressure results in opposite movement of the piston, whereby the barrier is retracted and blocks less of the opening. The use of hydraulically controlled valves, as opposed to pneumatically or electronically controlled valves, is preferred because the response time is much better.
This structure works well with systems in which the low pressure side is monitored, since the required movement of the solid barrier relative to the opening is directly responsive to the change in pressure, i.e., an increase in pressure causes the solid barrier to block more of the opening and a decrease in pressure causes the solid barrier to block less of the opening. This construction however is useless in flow situations where the upstream high pressure region needs to be monitored, and the compensating valve and homogenization orifice must adjust inversely to the change in pressure, i.e., where an increase in pressure and force against the piston of the compensating valve must result in a larger effective opening size in order to decrease upstream pressure, and a decrease in upstream pressure must result in a smaller effective opening size to increase effective opening size.
It is desirable in certain applications to have a piston type valve directly responsive to fluctuations in pressure in a fluid reservoir or conduit which is constructed to be utilized with very high pressures and where the travel of the piston within the compensating valve is not restricted to a small distance. It is an object of this invention therefore, to provide such a valve which can be operative in conjunction with fluid reservoirs or conduits having pressures up to about 2000 psi. It is a further object of this invention to provide such a valve in which the hydraulic fluid is sealed in the piston head cavity by the use of O-rings, in order to allow greater travel of the piston. It is a still further object to provide such a valve which comprises means in addition to the biasing spring to apply pressure against the pressure of the hydraulic fluid in order to reciprocate the piston, such means preferably being pressurized air introduced by a conduit through the piston casing to the underside of the piston head. It is another object to provide a valve suitably adapted to be utilized as part of a compensating valve system, and even more particularly as part of a compensating valve system having an adjustable homogenization orifice for mixing liquids, where the size of the homogenization orifice is adjusted in response to fluid pressure in a fluid reservoir or conduit. It is a still further object to provide a valve system where monitored pressure can be on either the high pressure or low pressure said of the homogenization orifice.